Electrostatic filter

ABSTRACT

An electrostatic filter for use in an air-cleaning appliance suitable for residential as well as industrial premises has electrodes separated by a substance which permanently adsorbs or absorbs the particles carried by the air, or converts them into innocuous compounds by a chemical transformation or reaction, so as to prevent the particles from being returned to the ambient air when the appliance is switched off. The substance may, for example, be one having a large surface area, such as activated carbon, kieselguhr zoltile, gels or the like, or an oxidizing or reducing agent, e.g., potassium permanganate or sodium persulphate, and may be applied in the form of a surface layer either to at least one of the electrodes or to a spacer element therebetween. To optimize the effectiveness of the substance, auxiliary heating may be provided if necessary. The spacer element, if provided, may be corrugated or folded so as to increase its surface area, the air passing along the corrugations or folds.

Elnited States Patent I1 1 Hundhausen et al.

[ Oct. 15, 1974 ELECTROSTATIC FILTER [76] Inventors: Eckhard Hundhausen, Pmfmry F Scovronek Asststant Exammer-Michael S. Marcus Margarethenstrasse 21, 6242 1 F R H Schlonberg Taunus; Claus Christian Attorney, Agent, or trm-Kar oss, erbert Cobarg, Rossertstrasse 28, 6374 Dubno Steinbach Taunus; Hans-Georg Boehm, Kellergrundweg 13, Kronberg Taunus, all of Germany An electrostatic filter for use in an air-cleaning appli- [22] Flled July 1972 ance suitable for residential as well as industrial prem- [21] Appl. No.: 275,685 ises has electrodes separated by a substance which permanently adsorbs or absorbs the particles carried by the air, or converts them into innocuous com- [30] Forelgn Apphcat lon Pnomy Dam pounds by a chemical transformation or reaction, so July 28, 1971 Austria 6576/71 as to prevent h particles f b i returned to h ambient air when the appliance is switched off. The [52] US. Cl 23/284, 23/252 R, 55/ 124, Substance may, f r l b e having a large sur- 55/132 55/135 55/155 face area, such as activated carbon, kieselguhr zoltile, [51] f Cl B03c 3/00 B03: 3/01 9/00 gels or the like, or an oxidizing or reducing agent, e.g., 2 2 .E'E'QPEFEH$LQE$Z 2Q potassium permanganate or sodium persulphate, and 557124 132, 134, 143, may be applied in the form ofa surface layer either to 154 at least one of the electrodes or to a spacer element therebetween. To optimize the effectiveness of the References Cited substance, auxiliary heating may be provided if neces- UNITED STATES PATENTS sary. The spacer element, if provided, may be corru- 1,964,794 7 1934 Gilbert 23/284 gated or folded so as to increase its Surface area, the 2,974,747 3 1961 Coolidge, Jr et 1 air passing along the corrugations or folds. 3,665,679 5/1972 McLain et al. 55 124 x 8 Cl 6 D F.

FOREIGN PATENTS OR APPLICATIONS 'l' gums 1,212,703 9/1966 Germany I l 1 I 77 :/i :/lj:; l

I J J 76 U A /U/U 7 2 INSERT LADEN WITH ACTIVE SUBSTANCE PATENTEDHBT 1 11 1 3.841.840

sum 10F 2 INSERT LADEN WITH 3 ACTIVE SUBSTANCE PAIENTEnncn 5:914 3L8 4'1 .840

" snmeurz CONVOLUTED ASSEMBLY OF ELECTRODES AND INSERT LADEN WITH ACTIVE SUBSTANCE Fl'g6 i /L Z Fig5 ELECTROSTATIC FILTER Our present invention relates to electrostatic filters for air purification, a term here understood in the general sense as the cleaning of air for breathing in enclosed spaces, by the removal of all kinds of matter suspended therein such as organic or inorganic dust, smoke particles and molecules of chemical compounds, particularly of aromatic and aliphatic hydrocarbons.

The electrostatic-filtering technology has so far essentially been developed for application in technical production establishments, particularly for cleaning of flue gases of heating appliances, blast-furnace gas and the like. The apparatus concerned is technically very elaborate and permanently installed in the smoke currents. More recently the electrostatic filter has also been applied to the improvement and cleaning of air in industrial and residential premises, for which purpose a fan causes air containing charged particles to flow under pressure or suction between filter electrodes to which a high D. C. potential is applied. The advantages of the electrostatic filter reside in its low resistance to flow and its high yield, even in the case of the smallest particles of the order of 10*;1. in size. The low flow resistance makes it possible to obtain an air throughput which is of adequate proportions for residential and industrial premises, even with small fans and low electricpower consumption. The large bandwidth of the filtering enables removal for the air to.be breathed even of suspended and olfactory matter whose presence, de-

pending on its quantity or resistance time, tends to have for this is that the bonds of such molecular compounds are only very weak (Vander-Waals type).

The object of the invention is therefore to improve the known electrostatic filter for the purpose of air cleaning in such a way that molecules of organic compounds which have been separated out either cannot re-evaporate from the filter electrodes or can do so only in an innocuous form.

In accordance with our invention, the space between confronting electrodes of opposite polarity in an electrostatic filter of the kind hereinbefore described is partly occupied by active substances which permanently adsorb, or absorb and/or convert into innocuous compounds by a chemical transformation, the particles moving to the filter electrodes in the D. C. field. By innocuous we mean such compounds which, as previously mentioned, have no adverse effect either on health or on comfort.

To accommodate the active substance or purifying agent between the filter electrodes, we dispose in the intervening space a foil-shaped insert acting as a carrier for that substance, the insert lying with its major surfaces parallel to the direction of the air flow circulating through-the intervening space; these major surfaces and the electrode faces define a plurality of unobstructed parallel channels through which the air can pass in'contact with the active substance carried thereon. Thus, the insert could be disposed with clearance parallel to the electrode faces; more advantageously, the insert is an undulating strip of sheet material with fold lines parallel to the flow direction contacting the electrode faces whereby the strip also acts as a spacer. Such an assembly of two electrodes and an interposed undulating spacer, laden with purifying agent, can also be convoluted to form a cylindrical filter cartridge. If desired, either or both electrode faces may also be coated with purifying agent.

Among the active substances usable as purifying agents in a system according to our invention there are first of all purely mechanically adsorbent substances having a large surface area, such as activated carbon, kieselguhr, zoelite, gels and the like; furthermore, particularly for the removal of the heavy molecules of aromatic compounds with unpleasant odors, all compounds which have an oxidizing or reducing effect thereon, preferably suchvwhich can be applied at room temperature in the presence of a catalyst so-called cold combustion or in special cases also such substances which have to be separately heated up to an elevated reaction temperature, may be used. Suitable purifying agents of the oxidizing type include potassium permanganate and sodium persulphate.

Although deodorizing 'filters with activated carbon and the like are known, the flow therethrough is trans verse the air flow. The use of such substances in accordance with the invention in an electrostatic filter itself instead of an auxiliary filter of conventional kind inserted upstream or downstream thereof, enables small appliances to be designed which have a high air throughput and improved filtering effect.

In the construction of a filter embodying the invention, a layer of dielectric is created betweenthe polarized'filter electrodes. This establishes certain 'electrical criteria for a suitable active substance i.e., that its dielectric losses be low and likewise its dielectric constant, so that the DC. field acting on the air passing through the filter and on theparticles contained therein is substantially formed in the residual free air gap between the filter electrodes.

The invention makes it possible to use electrostatic filters as in intermittently operated appliances for air cleaning in enclosed'space's either'exclusively or in addition to the conventional dust filters in which the current of air is transverse thereto, and to utilize the great advantages of electrostatic filters from the point of view of power consumption and the bandwidth of their specific effectiveness, without the filtered-off particles returning to the ambient air between periods of operation.

' Whenever as the active substances are saturated or spent, the insert laden therewith may be regenerated or cleaned and reloaded or, if neither is possible, replaced by a fresh insert.

Several embodiments of our invention will now be explained with reference to the accompanying drawing which represents greatly enlarged diagrammatic sectional views and in'which:

FIG. 1 shows a layer-carrying filter electrode,

FIG. 2 shows an insert spacedly disposed in an air gap between two filter electrodes;

FIG. 3 shows a modification of the arrangement of FIG. 2;

FIG. 4 is a fragmentary perspective view, partly in section, of a portable air-cleaning appliance equipped with an electrostatic filter embodying our invention.

FIG. is an axial sectional view, taken on the line V V of FIG. 6, of another filter-equipped appliance; and

FIG. 6 is a cross-sectional view taken on the line VI VI of FIG. 5.

In FIG. I, a section of a filter electrode 1 which here plate-shaped, is shown which defines an outer electrode of a set of electrodes and which has a layer of an active substance or purification agent 2, e.g. activated carbon, on its surface confronting an associated counterelectrode (not shown).

The filter electrode may be in the form of a metal plate, a metallized plastic plate or a foil and may preferably be in the form of a grid, whose interstices are filled with the active substance, or a metallized fabric, which is impregnated with the active substance. The active substance may also be conductive.

FIG. 2 shows an arrangement of the active substance on a carrier 4 inserted in the air gap 5 between the filter electrodes 1 and 3 of opposite polarity. The carrier is constructed in the manner hereinbefore described with reference to the electrode 1 of FIG. 1.

FIG. 3 shows a modification of the assembly of FIG. 2; here the carrier 6 for the active substance is arranged in undulating manner'in the air gap 5 for the purpose of increasing its surface and makes alternate line contact with the electrodes 1, 3.

The carrier 6 may, for example, consist of corrugated paper which has been impregnated with the active substance before or after its installation between the filter electrodes, or it may consist of a fabric which inherently has the required rigidity or which acquires it only after impregnation with the active substance.

These basic forms can be varied in detail. Thus, for example, a plurality of layers of the active substance may berelatively superimposed or a layered electrode in accordance with FIG. 1 can be combined with the assembly of FIG. 2 or 3; alternatively flat filters or wound filters, so-called filter cartridges, may be produced. I v

FIG. 4 shows a cross-section through a portable aircleaning appliance of a form which is known (per se e.g. as known from German Pat. specification No. l,2l2,703) for electrical auxiliary heating appliances for residential or working premises. In a housing 10 a so-called cross-flow fan is provided, i.e., a fan whose cylindrical rotor, provided with blades 110, has the air current passing through it twice. The air is sucked in through a grid 13 in the housing 11, and through a mechanical segregating filter 14 for coarse dust, hair, threads and the like, in the direction of the arrow F,

' through a low pressure chamber 18 and is again dislindrical rotor 11. The particles which are carried along by the air stream and move against one or both filter electrodes 1, 3, in the electrostatic field present between these electrodes, are permanently absorbed or chemically neutralized. After opening of the grid 13, the segregating filter 14 can be removed and cleaned. After opening of the frontal side 19 of the housing which contains the discharge slits 15, the carrier 17 may also, after a period 'of time in which the active sub stances have become spent, be exchanged.

FIG. 4 shows only diagramatically the preferably transportable air-cleaning appliance equipped with our improved electrostatic filter. Not shown are, for example, the stand or foot of the appliance which may be arranged on the underside of the housing 10, the motor which drives the fan shaft 111, and the supply unit which produces the high tension for the filter elec trodes l, 3 from an A.C. supply; the motor and the supply unit may, for example, be arranged on the end faces of the housing 10. Finally, means may also be provided in the discharge channel of the fan for heating, and humidifying the cleaned air.

In FIGS. 5 and 6 we have shown an appliance having a substantially cylindrical housing 20 to which an air current is applied axially, the latter being produced by an axial fan having a propeller 21 and a motor 22. The air is aispirated through an intercepting grid 23, and moves through the mechanical coarse filter 14, past the discharge electrodes 16 and then through a cluster of filter cartridges 24, shown in outline and arranged symmetricallyin a circle with their axes parallel to that of housing'20. The cartridges 24 have a coiled structure of the type illustrated in FIG. 3. The cleaned ajr leaves the housing20 through a discharge grid 25.

FIG. 6 shows detail of the discharge side of the appliance; The core of the appliance in the region of the filter cartridges 24 is taken up by a high-voltage power supply 26 (not shown in FIG. 6). Alternatively with an appropriate choice of diameters the core space may also be occupied by a further filter cartridge and the power pack may be accommodated, for example, in the stand (not shown).

As will be apparent from the illustrated embodiments, our invention displays considerable versatitlity and may be incorporated in a great variety of differently constructed appliances.

In cases where the chemical compounds used as the active substance exhibit their optimum effect at temperatures above room temperature and such operation is compatible with the mean velocity of the air to be cleaned and/or the length of the filter, the active sub stance and/or its carrier may also be heated directly or indirectly, e.g. by the provision of a heating resistance for the filter electrodes or of heating registers in the low-pressure chamber 18 (FIG. 4) or in the discharge channel upstream of the filter.

We claim: f v

1. An electrostatic filter comprising:

-a pair of spaced-apart electrodes with confronting faces energized with opposite polarity;

circulation means for driving a flow of air to be purified through the space between said electrodes; and

a foil-shaped insert disposed between said electrodes with major surfaces parallel to the direction of said flow, said major surfaces defining with said confronting faces a plurality of substantially unobstructed parallel channels, said insert being laden with a purifying agent exposed to the air flow along said major surfaces.

2. An electrostatic filter as defined in claim 1 wherein said insert is disposed with clearance between said electrodes, said major surfaces lying substantially parallel to said confronting faces.

'3. An electrostatic filter as defined in claim 1 wherein said insert is an undulating strip of sheet material with fold lines paralleling said direction of flow.

4. An electrostatic filter as defined in claim 3 wherein said strip contacts said confronting faces along said fold lines.

5. An electrostatic filter as defined in claim 4 wherein said electrodes and said insert are convoluted into a substantially cylindrical cartridge with an axis parallel to said direction of flow.

6. An electrostatic filter comprising a plurality of substantially cylindrical cartridges as defined in claim 5, a common housing for said cartridges and circulation means common to said cartridges in said housing.

7. An electrostatic filter as defined in claim 6 wherein said housing is substantially cylindrical and open at both ends of the cylinder, said cartridges being clustered in said housing with their axes parallel to the housing axis, said circulation means comprising'an axially oriented fan disposed near one of said ends.

8. An electrostatic filter as defined in claim 7, further comprising a charging grid interposed in said housing between said fan and said cartridges. 

1. AN ELECTROSTATIC FILTER COMPRISING: A. PAIR OF SPACED-APART ELECTRODES WITH CONFRONTING FACES ENERGIZED WITH OPPOSITE POLARITY; CIRCULATION MEANS FOR DRIVING A FLOW OF AIR TO BE PURIFIED THROUGH THE SPACE BETWEEN SAID ELECTRODES; AND A FOIL-SHAPED INSERT DISPOSED BETWEEN SAID ELECTRODES WITH MAJOR SURFACES PARALLEL TO THE DIRECTION OF SAID FLOW, SAID MAJOR SURFACES DEFINING WITH SAID CONFRONTING FACES A PLURALITY OF SUBSTANTIALLY UNOBSTRUCTED PARALLEL CHANNELS, SAID INSERT BEING LADEN WITH A PURIFYING AGENT EXPOSED TO THE AIR ALONG SAID MAJOR SURFACES:
 2. An electrostatic filter as defined in claim 1 wherein said insert is disposed with clearance between said electrodes, said major surfaces lying substantially parallel to said confronting faces.
 3. An electrostatic filter as defined in claim 1 wherein said insert is an undulating strip of sheet material with fold lines paralleling said direction of flow.
 4. An electrostatic filTer as defined in claim 3 wherein said strip contacts said confronting faces along said fold lines.
 5. An electrostatic filter as defined in claim 4 wherein said electrodes and said insert are convoluted into a substantially cylindrical cartridge with an axis parallel to said direction of flow.
 6. An electrostatic filter comprising a plurality of substantially cylindrical cartridges as defined in claim 5, a common housing for said cartridges and circulation means common to said cartridges in said housing.
 7. An electrostatic filter as defined in claim 6 wherein said housing is substantially cylindrical and open at both ends of the cylinder, said cartridges being clustered in said housing with their axes parallel to the housing axis, said circulation means comprising an axially oriented fan disposed near one of said ends.
 8. An electrostatic filter as defined in claim 7, further comprising a charging grid interposed in said housing between said fan and said cartridges. 